Compositions for planarizing or polishing the surface of a substrate are well known in the art. Polishing slurries typically contain an abrasive material in an aqueous solution and are applied to a surface by contacting the surface with a polishing pad saturated with the slurry composition. Typical abrasive materials include silicon dioxide, cerium oxide, aluminum oxide, zirconium oxide, and tin oxide. U.S. Pat. No. 5,527,423, for example, describes a method for chemically-mechanically polishing a metal layer by contacting the surface with a polishing slurry comprising high purity fine metal oxide particles in an aqueous medium.
Conventional polishing compositions typically are not entirely satisfactory at polishing and/or planarizing corundum (crystalline Al2O3), including artificial and natural sapphires and rubies, particularly those used for laser and light-emitting diode (LED) applications, or at polishing and/or planarizing GaAs, GaP and GaAs/GaP alloys. In particular, polishing slurries can have less than desirable polishing rates, and their use in chemically-mechanically polishing semiconductor surfaces can result in poor surface quality. Because the performance of a semiconductor wafer is directly associated with the planarity of its surface, it is crucial to use a polishing composition that has a high polishing efficiency, uniformity, and removal rate and leaves a high quality polish with minimal surface defects.
The difficulty in creating an effective polishing composition for corundum, GaAs, GaP and GaAs/GaP alloys, particularly colorless sapphire wafers that have been artificially synthesized for laser and LED applications stems from the complexity of balancing polishing efficiency and surface quality. The corundum, GaAs, GaP and GaAs/GaP alloy wafers used in laser and semiconductor industry need to be polished smoothly and defect-free at the nanoscale level for their application. It has been a continuous challenge for manufacturers to achieve the required surface smoothness at an economical rate.
There have been many attempts to improve the polishing efficiency and uniformity of conventional polishing agents, while minimizing defects in the polished surface and damage to underlying structures or topography. For example, U.S. Pat. No. 5,340,370 describes a polishing composition comprising an abrasive, an oxidizing agent, and water, which purportedly yields an improved removal rate and polishing efficiency. Similarly, U.S. Pat. No. 5,622,525 describes a polishing composition comprising colloidal silica having an average particle size of 20-50 nm, a chemical activator, and demineralized water.
A need remains, however, for compositions and methods that will exhibit desirable planarization efficiency, uniformity, and removal rate during the polishing and planarization of substrates, particularly corundum, GaAs, GaP and GaAs/GaP alloy semiconductor wafer surfaces, while minimizing defects, such as surface imperfections and damage to underlying structures and topography during polishing and planarization.